Zhuojin Pipe Fitting Co., LtdElectroslag Overlay of Powder Materials on Cutting Tools
Literature Overview
The article "Electroslag Overlay of Powder Materials on Cutting Tools" by Ni Xiaolei, published in "Machine Design and Manufacturing" in 1993 (Issue 1, pages 45-46), presents a fascinating application of electroslag welding (ESW) technology to the overlay of refractory compound materials onto steel tool shanks. Classified under TG455, this work describes a technique developed at the Volgograd Engineering Structures Institute, building upon methods provided by the EO Paton Electric Welding Institute in Ukraine. The abstract highlights a key challenge: the poor wettability of molten steel against refractory compounds, which complicates the overlay process. The authors developed an innovative solution using a non-consumable tungsten electrode to deposit specially composed materials containing carbide and boride particles onto cutting tool shanks.
Core Technical Content and Process Description
The fundamental problem addressed in this article is the difficulty of achieving metallurgical bonding between a steel tool shank and a refractory compound overlay, such as a carbide or boride-based wear layer. The poor wettability of steel against these refractory materials means that conventional arc welding processes often produce incomplete fusion, leading to weak interfaces and premature delamination of the overlay. The electroslag welding process, with its characteristic slow cooling rates and deep penetration, offers a unique opportunity to overcome this challenge by creating a controlled thermal environment that promotes interfacial bonding.
The technique described uses a non-consumable tungsten electrode with a diameter of 5 mm and a length of 600 mm. The overlay material is fed as a powder with a specific particle size distribution: fine particles (1-5 μm) comprising 30% of the mix, medium particles (5-10 μm) comprising 40%, and coarse particles (20-25 μm) comprising 28%. The remaining 2% likely represents a binder or flux component. The powder is first dry-mixed to ensure uniform distribution before being fed into the welding zone.
| Parameter | Specification | Purpose |
|---|---|---|
| Electrode material | Non-consumable tungsten | Provides stable arc without dilution |
| Electrode diameter | 5 mm | Balances arc stability and penetration |
| Electrode length | 600 mm | Allows continuous feeding |
| Fine particles (1-5 μm) | 30% | Promotes bonding and fills interstices |
| Medium particles (5-10 μm) | 40% | Primary structural component |
| Coarse particles (20-25 μm) | 28% | Provides wear resistance |
| Mixing method | Dry mixing | Ensures uniform particle distribution |
The use of a non-consumable tungsten electrode is a key innovation in this process. By eliminating the consumption of the electrode, the process avoids the dilution of the overlay material with electrode metal, ensuring that the deposited layer retains its designed composition and properties. The tungsten electrode serves solely to maintain the arc and transfer heat to the powder material, which melts and deposits onto the tool shank.
Metallurgical Considerations
The metallurgical challenge of overlaying refractory compounds onto steel is fundamentally one of interfacial bonding. The poor wettability of steel against carbides and borides means that the molten powder must be carefully controlled to achieve intimate contact with the base metal. The electroslag process, with its slag flux covering the weld pool, creates a protective atmosphere that prevents oxidation and allows for slow, controlled solidification. The slow cooling rate promotes the formation of a diffusion bond at the interface, where atomic diffusion between the steel and the refractory compound creates a metallurgical bond rather than a mere mechanical one.
The particle size distribution of the overlay powder is critical to the process success. The fine particles (1-5 μm) serve to fill the interstices between larger particles and promote wettability by increasing the contact area with the base metal. The medium particles (5-10 μm) form the bulk of the deposit and provide the primary wear-resistant structure. The coarse particles (20-25 μm) contribute to wear resistance through their hardness and size, but their presence must be balanced against the risk of poor bonding due to their limited wettability. The dry mixing process ensures that the particle size distribution is maintained throughout the powder supply, preventing segregation that could lead to inconsistent deposit composition.
Process Parameters and Quality Control
The electroslag welding process parameters for this application include the welding current, voltage, travel speed, and powder feed rate. The welding current is typically in the range of 200-400 A, depending on the thickness of the overlay layer and the size of the tool shank. The voltage is maintained at a level that ensures stable slag formation and adequate penetration into the base metal. The travel speed must be carefully controlled to ensure that the powder is fully melted and deposited without excessive burning or incomplete fusion.
Quality control of the overlay weld is essential to ensure the durability of the cutting tool. The interface between the overlay and the base metal should be examined metallographically to confirm complete fusion and the absence of cracks or porosity. Hardness testing across the overlay layer should reveal a uniform hardness profile, with a slight gradient near the fusion line due to dilution. The overlay thickness should be measured to ensure it meets the specified minimum, as insufficient thickness would provide inadequate wear protection.
Engineering Practice and Applications
The electroslag overlay of refractory compounds onto cutting tools is applicable in a range of industrial scenarios where tool life extension is economically important. In mining operations, where rock drills and cutting tools are subjected to extreme abrasion, overlay welding can extend tool life by several times. In metalworking, where cutting tools are used for machining hard materials, overlay welding can provide a wear-resistant surface that maintains cutting edge geometry for longer periods.
The process described in this article has particular relevance to the manufacture of heavy-duty cutting tools such as rock drill bits, mining picks, and industrial saw blades. The combination of a tough steel shank with a hard, wear-resistant overlay provides the best of both worlds: structural integrity from the base metal and wear resistance from the overlay. The use of a non-consumable electrode ensures that the overlay composition is not compromised by dilution, which is a significant advantage over consumable electrode processes.
Study Insights and Reflections
This article by Ni Xiaolei presents a technically sophisticated solution to a challenging metallurgical problem. The use of electroslag welding for overlay applications is not widely known outside of specialized welding communities, and this work serves as an excellent introduction to the technique's potential. The innovation of using a non-consumable tungsten electrode to avoid dilution is particularly elegant and demonstrates the kind of creative problem-solving that advances our field. The careful attention to particle size distribution and dry mixing methodology reflects a deep understanding of the relationship between powder characteristics and deposit properties. For engineers working in tool manufacturing and surface engineering, this work highlights an underutilized process that could significantly extend the service life of critical cutting tools. The principles described here—controlled thermal input, particle size optimization, and interface bonding through diffusion—are broadly applicable to other overlay welding challenges and deserve wider recognition in our engineering community.